In magnetic recording disk drives, data is stored in a thin magnetic layer on the disk. Data is written to and read from the disk by a recording head at the back of a slider flying in close proximity to the magnetic layer at high speeds.
The magnetic recording disk typically comprises a substrate, such as a disk blank made of glass or an aluminum-magnesium (AlMg) alloy with a nickel-phosphorous (Ni--P) surface coating, a cobalt-based magnetic alloy film formed by sputter deposition over the substrate, and a sputter-deposited underlayer, such as a layer of chromium (Cr) or a chromium-vanadium (Cr--V) alloy, between the substrate and the magnetic layer. A protective overcoat, such as a sputter-deposited amorphous carbon film, is formed over the magnetic layer to provide corrosion resistance and wear resistance from the slider. In contact start-stop (CSS) types of disk drives the slider is at rest on the disk when the drive is started and comes to rest on the disk when the drive is stopped. A liquid perfluoropolyether (PFPE) lubricant is also maintained on the surface of the protective disk overcoat to prevent damage to the head and the disk during starting and stopping of the disk.
Protective carbon overcoats for thin film disks are well known. They are typically formed by sputter deposition from a graphite target, and are generally called protective carbon overcoats, "diamond-like" carbon overcoats, amorphous carbon overcoats, or in the case of those overcoats formed by sputter deposition in the presence of a hydrogen-containing gas, hydrogenated carbon overcoats. Tsai et al. in "Structure and Properties of Sputtered Carbon Overcoats on Rigid Magnetic Media Disks," J. Vac. Science Technology, A6(4), July/August 1988, pp. 2307-2314, describe such protective carbon overcoats and refer to them as amorphous "diamond-like" carbon films, the "diamond-like" referring to their hardness rather than their crystalline structure. U.S. Pat. No. 4,778,582, assigned to IBM, describes a protective hydrogenated disk carbon overcoat formed by sputtering a graphite target in the presence of Ar and hydrogen (H.sub.2). The carbon overcoats may also be formed by plasma-enhanced chemical vapor deposition (CVD) and may include nitrogen in addition to hydrogen, as described by Kaufman et al., Phys. Rev. B, Vol. 39, p. 13053 (June 1989).
To increase the areal density of the data magnetically recorded on the disk, the recording head must be brought close to the magnetic layer, which means that the overcoat thickness must be substantially reduced, i.e., to less than 5 nm in future disk drives. Consequently, an important challenge faced by the disk drive industry is how to make protective disk overcoats that are ultra-thin yet still provide the desired durability and corrosion protection. A major obstacle to reducing the overcoat thickness is that, in order to achieve good magnetic recording characteristics, the magnetic layer must usually be formed on a slightly roughened or textured substrate. Yet, in order to achieve good durability and corrosion protection, the smoothest final disk surface is desired.
What is needed is an ultra-thin disk overcoat that can provide improved durability and corrosion protection while also providing a planarized final disk surface.